High Resolution Detectors for Single Photon Cardiac Imaging Single photon emission computed tomography (SPECT) is a powerful, noninvasive medical imaging modality that mathematically reconstructs the three dimensional distribution of a radionuclide throughout the body of a human patient or a research animal. Typically, the collected data are displayed and evaluated as a set of two-dimensional images through the organ or diseased area under investigation. SPECT allows quantitative study of the function in the investigated region and therefore is an extremely useful tool for understanding organ and tissue physiology including that in the heart. SPECT is very commonly used in identifying as well as localizing coronary artery disease and as many as 90% of all myocardial perfusion studies are now performed using SPECT. Thus, SPECT is playing a critical role in cardiac imaging, providing both diagnosis as well as prognosis. However, there is urgent need for improvement in the instrumentation that is currently used for this imaging modality and expand its capabilities in order to exploit its full potential. At present, the performance of SPECT systems often is limited by the detectors used in these systems. Modern SPECT systems consist of scintillation crystals coupled to photomultiplier tubes as detectors. Important requirements for scintillators used in SPECT applications include high light output and high energy resolution, reasonably fast response and high gamma ray stopping efficiency. Ideally, the scintillator should also be inexpensive, rugged and easy to manufacture. Currently, NaI(Tl) is the detector of choice in SPECT systems and it is relatively inexpensive and its light output is fairly large. However, the poor energy resolution of NaI(Tl) often limits SPECT performance. The energy resolution of NaI:Tl is limited by its relatively poor proportionality. If scintillators with higher energy resolution at typical SPECT energies (~140 keV) were available, the essential process of scatter rejection would improve. Furthermore, dual-isotope imaging, which is a unique property of SPECT, would also become possible if scintillators with high energy resolution became available. The goal of the proposed effort is to investigate a new high resolution detector for SPECT studies. Enhanced scatter rejection can be expected along with possibility of dual isotope imaging. The Phase I project will be aimed at demonstrating the feasibility of the proposed concept, while the Phase II project will be aimed at optimization of the new detector, implementation of the prototype module and detailed performance evaluation.